Substantial Equivalence: Choosing and Defending a Predicate
A 510(k) does not argue that your device is safe and effective. It argues that it is substantially equivalent to a device already legally on the market, called the predicate.
Everything in the submission serves that comparison. Choose the predicate badly and no amount of testing rescues the file.
The test
A device is substantially equivalent if it has the same intended use as the predicate, and either:
- the same technological characteristics, or
- different technological characteristics that do not raise different questions of safety and effectiveness, and where the information submitted demonstrates the device is at least as safe and effective as the predicate.
Where files fail
Intended use drift. Your device does something slightly more, or for a slightly different population, than the predicate. Intended use is the first gate and there is no partial credit: a different intended use ends the comparison.
Different technology, unexamined. New material, new energy source, new software function. That is allowed, but it shifts the burden to you to show it raises no different questions, and to bring the data that closes them.
Split predicates. Taking the intended use from one device and the technology from another is not permitted. FDA calls this a split predicate and will not accept it. A reference device is different and is allowed: it supports a specific scientific question, not the equivalence argument itself.
Choosing a predicate
The instinct is to pick the closest device. Better questions:
- Is it still legally marketed? A predicate that has been withdrawn for safety reasons is a poor foundation, and FDA's 2018 policy discourages relying on very old predicates.
- How old is it? Citing a predicate cleared decades ago invites scrutiny of whether it still represents current technology.
- What was its own predicate? Chains matter. A predicate whose clearance rests on a device later recalled is a weak base.
- Does its intended use statement actually match yours, word for word, rather than approximately?
Searching the 510(k) database by product code rather than by device name is usually how you find the real candidates.
If there is no predicate
Then substantial equivalence is unavailable, and the device is Class III by statute. The routes are De Novo for novel low-to-moderate risk devices, or PMA.
An NSE determination, not substantially equivalent, also opens a 30 day window to request De Novo classification.
Frequently asked questions
What is substantial equivalence?
The finding that a device has the same intended use as a legally marketed predicate and either the same technological characteristics, or different ones that raise no different questions of safety and effectiveness.
What is a predicate device?
A legally marketed device used as the comparison in a 510(k).
Can I use two predicates?
You may cite multiple predicates for a device with multiple functions, but you may not split intended use from one and technology from another.
What is a reference device?
A device cited to support a specific scientific question rather than the equivalence argument. It is permitted where a split predicate is not.
Does substantial equivalence mean identical?
No. Different technological characteristics are allowed if they raise no different questions of safety and effectiveness and you bring data.
What happens if FDA finds my device NSE?
The 510(k) is not cleared. You may request De Novo classification within 30 days, submit a new 510(k) with a different predicate, or pursue PMA.